The present invention relates to a pickup lens for an optical disk which is used for reading information from a storage medium, or recording, mainly by using a laser beam, and in particular, to a pickup lens for an extremely small optical disk.
There are various formats (specifications) for information recording media available on the market, and various technologies are employed and studied for the various formats.
In recent years, in particular, a broadband has become popular to create a broadband age, and there are circulating high-volume contents of images, animations and sounds. It is therefore necessary, even for general users, to stock high-volume data.
With respect to a recording medium for data stocking, original ones were those wherein audio cassette tapes were used, and FD (floppy disk) is still used even today. In recent years, Zip (high-volume floppy disk having the measure of capacity of 100 M–200 M), MO (photo-electro-magnetic disk having the measure of capacity of 640 M–2.3 G), CD (optical disk having the measure of capacity of 640–700 M) and DVD (optical disk having the measure of capacity of 4.7 G) are used, which shows that the measure of capacity has grown great.
Among the aforesaid recording media, those utilizing light have their own optical systems.
The optical disks mentioned above have started from the music CD, and therefore, it is always necessary for the DVD which is becoming a leading recording medium now to consider interchangeability with CD, and a size of the DVD is large, which makes it difficult to provide a small-sized equipment, resulting in a problem. To solve this problem, a small-sized medium in a size of 8 cm and a deformed medium having a size of a business card have made an appearance, but it is unavoidable that they have less capacity.
Further, the DVD has a problem that many standards concerning information recording are present and interchangeability between them is insufficient.
With respect to the photo-electro-magnetic disk, problems of interchangeability with standards for low volume and problems that a size of a medium restricts a size of equipment remain unchanged, although the measure of capacity has been made great.
For those problems, there has been proposed a standard concerning a small-sized recording medium which is quite novel.
However, when a medium is small in size, an optical pickup lens and a unit are required to be small in size.
When an optical pickup lens and a unit are made to be small in size, manufacturing, assembling and adjustment of the lens itself become extremely difficult.